Polymer sustained-release coating fertilizer

Abstract

The application relates to the technical field of fertilizers, and discloses a high-molecular slow-release coating fertilizer and a preparation method of the high-molecular slow-release coating, which comprises the following steps: S1, dissolving polyamide in N,N-dimethylformamide, adding a polyacrylic acid solution, adding benzoyl peroxide as a free radical initiator, and carrying out grafting reaction; S2, adding long-chain alkyl bromide in the grafted polymer, carrying out hydrophobic modification, slowly adding polyethylene glycol after stirring for 0.5-1.5 hours, carrying out hydrophilic control, and continuing to stir for 2-4 hours. The method of grafting modification of polyamide by polyacrylic acid increases the interaction between the fertilizer components and the polymer, the proportion of the hydrophobic and hydrophilic groups in the polymer is controlled, the release of the fertilizer is slowed down, and the pollution caused by excessive use of the fertilizer is reduced.

Description

Technical Field

[0001] The invention relates to the technical field of fertilizers, in particular to a polymer slow-release coating fertilizer. Background Art

[0002] In modern agricultural production, fertilizer use is a key factor in increasing crop yields. However, traditional fertilizers, especially fast-release fertilizers, have certain problems. For example, they release nutrients too quickly, resulting in a large amount of nutrients being lost to crops through rainwater. This not only reduces fertilizer efficiency but can also lead to environmental problems such as eutrophication. Therefore, developing fertilizers that can effectively control the nutrient release rate to match the rate of crop absorption is of great significance for promoting sustainable agricultural development.

[0003] In recent years, with advances in materials science, polymers, due to their unique physical and chemical properties, have been widely researched and applied in the field of slow-release fertilizers. These polymers can be physically or chemically combined with fertilizer ingredients to form slow-release systems, extending the duration of nutrient release. Currently, most slow-release coated fertilizers on the market use synthetic polymers or natural polymers as carriers. These materials can, to a certain extent, control the release rate of fertilizers and reduce nutrient loss.

[0004] However, although existing technologies have made certain progress, how to further optimize the performance of polymer materials to adapt to the needs of different crops and soil environments remains a key issue that needs to be addressed in the development of agricultural fertilizer technology. Summary of the Invention

[0005] In response to the shortcomings of the existing technology, the present invention provides a polymer slow-release coated fertilizer that can effectively control the release rate of nutrients in agricultural fertilizers to improve the use efficiency of fertilizers, reduce environmental pollution, and enhance the economic benefits of agricultural production.

[0006] To achieve the above objectives, the present invention is implemented through the following technical solutions: A method for preparing a polymer sustained-release coating comprises the following steps:

[0007] S1. Grafting reaction

[0008] In this step, polyamide is dissolved in N,N-dimethylformamide (DMF) to form a solution. A polyacrylic acid solution is then added, and benzoyl peroxide is used as a free radical initiator to initiate the grafting reaction. The carboxyl groups (-COOH) of the polyacrylic acid are grafted onto the polyamide chains via a free radical mechanism, forming a new copolymer. This step increases the polymer's functional groups, thereby enhancing its ability to interact with fertilizer components.

[0009] The increased carboxyl groups can form stronger ionic bonds with cations in fertilizers (such as ammonium, potassium, etc.), thereby reducing the dissolution rate of nutrients in the fertilizer and achieving a slow-release effect.

[0010] S2. Hydrophobicity and hydrophilicity regulation

[0011] After the polymer grafting reaction is complete, a long-chain alkyl bromide is added for hydrophobic modification. This step adds hydrophobic groups to the polymer surface, reducing the affinity of the polymer for water. After stirring for 0.5 to 1.5 hours, polyethylene glycol is slowly added to adjust the hydrophilicity. Stirring is continued for 2 to 4 hours. The polyethylene glycol increases the hydrophilicity of the polymer, helping it absorb and retain more water. However, due to the previous hydrophobic modification, this water is not easily released.

[0012] This combined regulation of hydrophobicity and hydrophilicity enables the fertilizer to exist stably in a humid environment after absorbing water, prolongs the release time of water and nutrients, and reduces nutrient loss caused by too rapid release.

[0013] This technical solution enables precise controlled release of fertilizer nutrients, effectively extending the nutrient supply cycle and reducing environmental pollution caused by fertilizer loss. Polymer slow-release coated fertilizers using this coated slow-release material are not only suitable for a wide variety of crops but also highly adaptable to various environments, particularly in rainy or irrigated areas. Furthermore, by controlling nutrient release, farmers can reduce the frequency of fertilization, lowering labor costs and increasing economic returns. This also reduces the pressure on ecosystems caused by agricultural activities, providing effective support for the development of sustainable agriculture.

[0014] Preferably, the polyamide is prepared by the polycondensation reaction of caprolactam and water, which involves reacting caprolactam with an appropriate amount of water at elevated temperature to form a polyamide polymer.

[0015] The polycondensation reaction temperature is 240-280°C, a range designed to achieve optimal molecular weight and degree of polymerization. Temperatures that are too low may result in incomplete reaction, resulting in low polymer molecular weight and hindering subsequent modification. High temperatures, on the other hand, may lead to side reactions such as cross-linking or degradation, compromising product quality.

[0016] The duration is 10 to 14 hours, which is determined based on the reaction kinetics of polyamide and actual operating experience. A longer reaction time helps complete the polymerization reaction and ensures the uniformity and stability of the polymer chain.

[0017] After the polymerization reaction is complete, the polymer needs to be slowly cooled from the high temperature environment to room temperature to prevent sudden changes in physical structure caused by rapid temperature changes. The cooled polymer is usually in a lumpy or viscous state.

[0018] The cooled polymer is cut into small particles to facilitate subsequent processing and application. The particle size directly affects the efficiency and uniformity of the grafting modification. The appropriate particle size can increase the surface area for the grafting reaction, thereby enhancing the modification effect.

[0019] The above technical solution systematically optimizes the physical and chemical properties of polyamide, providing a high-quality substrate for subsequent grafting modification. The resulting polyamide exhibits improved chemical stability and mechanical properties, enabling it to exhibit superior nutrient-controlled release and environmental adaptability in applications such as polymer slow-release coated fertilizers.

[0020] Preferably, the molecular weight of the polyacrylic acid is 80,000 to 120,000.

[0021] The molecular weight of polyacrylic acid within the preferred range can ensure sufficient chain length for more effective grafting reaction with polyamide. A higher molecular weight helps form a stable polymer network rather than simple physical mixing, thereby improving the slow-release ability of the fertilizer at the chemical level.

[0022] The high molecular weight polyacrylic acid forms a complex and stable network within the polyamide matrix, effectively controlling the release rate of nutrients from the fertilizer. This structure limits the rapid diffusion of water and nutrients, enabling a slow release of nutrients that meets the needs of crop growth.

[0023] Within this molecular weight range, polyacrylic acid maintains good handling and rheological properties, facilitating processing and application in industrial production. At the same time, it ensures the mechanical strength and durability of the polymer, making it suitable for use in a variety of soil and climate conditions and not susceptible to degradation due to environmental factors.

[0024] Through the above technical solution, while ensuring the grafting reaction and sustained-release effect, the cost of the product can also be appropriately controlled.

[0025] Preferably, in the polyacrylic acid grafting reaction, the weight ratio of polyamide to polyacrylic acid is 0.5:1 to 1:1.

[0026] When the weight ratio of polyamide to polyacrylic acid approaches 1:1, sufficient polyacrylic acid molecules are available for grafting reaction with the polyamide, increasing the chances of reaction and forming a denser graft network. This helps enhance the structural stability of the polymer and improve the fertilizer's slow-release properties. A higher polyacrylic acid ratio (close to 1:1) forms a stronger ionic crosslinking network within the polymer. This network structure can more effectively control the release of nutrients from the fertilizer, preventing rapid nutrient loss and thus extending the duration of nutrient supply.

[0027] At a weight ratio as low as 0.5:1, although the amount of polyacrylic acid is relatively low, it is still sufficient to achieve effective grafting and reduce usage costs, making it suitable for cost-sensitive applications. Although the graft density is slightly lower at a lower ratio (0.5:1), it still provides a slow-release effect that is improved over conventional fertilizers while maintaining a low material cost.

[0028] Through the above technical solutions, the method of the present invention can flexibly respond to different agricultural needs and environmental conditions, achieving optimized fertilizer performance. This ratio range allows manufacturers to select the most appropriate ratio based on specific application requirements and cost control needs, ensuring that the fertilizer product provides excellent slow-release effects while maintaining economic production and application.

[0029] Preferably, the reaction temperature in the polyacrylic acid grafting reaction is 90-100° C., and the duration is 4-6 hours.

[0030] Reaction temperature (90-100°C):

[0031] This temperature range is considered ideal because it is above the glass transition temperature (Tg) of polyacrylic acid, allowing the polyacrylic acid segments to have sufficient mobility in solution to promote efficient contact and chemical reaction of the polyamide chains.

[0032] Setting the temperature within this range can prevent excessive heat from causing polymer degradation or premature reaction termination, while being sufficient to activate the benzoyl peroxide initiator, effectively generating free radicals and promoting the grafting reaction.

[0033] Duration (4-6 hours):

[0034] This time range is based on the need to achieve sufficient grafting of polyacrylic acid and polyamide. A time that is too short may result in incomplete grafting, while a time that is too long may increase production costs or even cause unwanted side reactions such as cross-linking or degradation.

[0035] A reaction time of 4 to 6 hours allows the polymer chains sufficient time to form stable chemical bonds while keeping the system energy and cost efficient.

[0036] Through the above technical solution, the prepared polymer slow-release coated fertilizer is not only technically feasible, but also has obvious advantages in economic and environmental benefits, which helps to promote its use in modern sustainable agricultural practices.

[0037] Preferably, in the hydrophobic modification, the long-chain alkyl bromide used is dodecyl bromide.

[0038] Dodecyl bromide (C12H25Br) is a commonly used hydrophobic surfactant. Its long hydrophobic chains can be effectively embedded in the polymer structure, enhancing the hydrophobicity of the entire polymer network through hydrophobic interactions.

[0039] This substance not only provides a hydrophobic effect in the polymer, but also interacts with other functional groups in the polymer due to the presence of bromide ions, further stabilizing the structure.

[0040] By introducing dodecyl bromide, the polymer's hydrophobicity is enhanced, making it difficult for water to penetrate the polymer matrix, thereby controlling the release rate of nutrients from the fertilizer. This controlled release mechanism is particularly suitable for crops that require long-term nutrition, providing continuous nutrient support throughout the growth cycle.

[0041] Through the above technical solution, the purpose of optimizing fertilizer release performance and enhancing environmental adaptability is achieved by changing the hydrophobic properties of the polymer.

[0042] Preferably, in the hydrophobicity modification and hydrophilicity regulation steps, the reaction temperature is 65-75°C.

[0043] Within the temperature range of 65°C to 75°C, chemical reactions proceed efficiently without being too rapid or intense, which helps control the reaction rate and ensure uniform hydrophobic and hydrophilic modification reactions. This temperature control helps avoid polymer degradation or undesirable side reactions that may occur due to excessively high temperatures.

[0044] Through the above technical solution, the reaction temperature of hydrophobic modification and hydrophilic regulation is preferably set at 65°C to 75°C in order to ensure the effectiveness and safety of the chemical reaction, as well as the quality and performance of the obtained polymer slow-release coated fertilizer, to meet the demand of modern agriculture for efficient and environmentally friendly fertilizers.

[0045] Preferably, in the hydrophilicity regulating step, the molecular weight of the polyethylene glycol selected is 3,000 to 5,000.

[0046] A polyethylene glycol molecular weight of 3,000 to 5,000 is selected to provide sufficient hydrophilicity while avoiding the increased viscosity and handling difficulties that can result from higher molecular weights. Polyethylene glycol in this molecular weight range effectively increases the polymer's hydrophilicity, helping it form a stable hydration layer upon contact with soil moisture, thereby controlling the slow release of water and nutrients.

[0047] This molecular weight range of polyethylene glycol ensures good dispersibility and compatibility in the polymer matrix, helping to maintain the overall mechanical strength and structural integrity of the polymer. This is because too low a molecular weight may not form an effective hydration layer, while too high a molecular weight may make the polymer too viscous, affecting its subsequent handling and application.

[0048] Through the above technical solution, polyethylene glycol with a molecular weight of 3,000 to 5,000 is selected for hydrophilicity regulation, which can not only effectively improve the water retention capacity and slow-release performance of the fertilizer, but also help achieve the economic efficiency of the production process and the environmental protection goals of the product.

[0049] The present invention also provides a polymer slow-release coating fertilizer prepared by the method. The polymer slow-release coating fertilizer comprises core NPK fertilizer particles and a polymer slow-release coating coated on the outside of the core NPK fertilizer particles.

[0050] Preferably, the preparation of the polymer slow-release coating fertilizer includes:

[0051] The modified polymer is mixed with NPK fertilizer in a mass ratio of 0.01:1 to 0.05:1 and granulated at a controlled temperature of 70-90°C. This temperature control ensures the stability of the physical properties of the polymer and fertilizer, while optimizing the morphology and size of the granules to suit the fertilization requirements of agricultural machinery.

[0052] The mixing and granulation steps ensure uniform distribution of the polymer and fertilizer components, improving the mechanical application performance of the fertilizer and the efficiency of nutrient absorption by the crop. Granulation also helps to reduce dust, prevent fertilizer agglomeration, and minimize nutrient losses during storage.

[0053] The present invention provides a polymer slow-release coating fertilizer. It has the following beneficial effects:

[0054] 1. This invention utilizes a polyacrylic acid grafting method to modify polyamide, enhancing the interaction between fertilizer components and the polymer. In particular, the introduction of functional carboxyl groups strengthens the ionic bond with the fertilizer components. This modified polymer significantly improves fertilizer utilization by more effectively controlling the rate of nutrient release, ensuring a slow and continuous nutrient supply throughout the plant's growth cycle, reducing nutrient loss and waste caused by rapid nutrient release.

[0055] 2. By controlling the ratio of hydrophobic and hydrophilic groups in the polymer, this invention not only slows fertilizer release but also reduces environmental pollution caused by excessive fertilizer use. The combination of hydrophobic and hydrophilic modification optimizes fertilizer interaction with soil and water, reducing the risk of nutrient leakage into water bodies through surface runoff and deep percolation, thereby protecting groundwater quality and the ecological safety of nearby water bodies. DETAILED DESCRIPTION

[0056] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0057] Example 1:

[0058] Materials and proportions:

[0059] Polyamide: prepared by polycondensation of caprolactam and water at a temperature of 250°C for 12 hours. The obtained polyamide is cooled and cut into pellets.

[0060] Polyacrylic acid (PAA): molecular weight 100,000, weight ratio to polyamide 1:1.

[0061] Benzoyl peroxide: acts as a free radical initiator.

[0062] Dodecyl bromide: used for hydrophobic modification.

[0063] Polyethylene glycol (PEG): molecular weight 4,000, used for hydrophilicity regulation.

[0064] NPK fertilizer: The mass ratio to modified polyamide is 0.03:1.

[0065] Preparation steps:

[0066] 1. Polyacrylic acid grafting reaction: Dissolve polyamide in N,N-dimethylformamide, add polyacrylic acid solution, and carry out grafting reaction at 95°C for 4 hours.

[0067] 2. Hydrophobic modification and hydrophilic regulation: 10% dodecyl bromide was added, stirred for 1 hour, and then 7% polyethylene glycol was gradually added. The total stirring time was 4 hours, and the reaction temperature was 70°C.

[0068] 3. Mixing and granulation: The modified polymer is mixed with the NPK fertilizer and granulated using an extruder at 80°C.

[0069] Example 2:

[0070] Compared with Example 1, the difference is:

[0071] Materials and proportions:

[0072] Polyamide: reaction temperature 260°C, duration 14 hours.

[0073] Polyacrylic acid (PAA): molecular weight 120,000, weight ratio to polyamide 0.5:1.

[0074] NPK fertilizer: The mass ratio to modified polyamide is 0.05:1.

[0075] Preparation steps:

[0076] 1. Polyacrylic acid grafting reaction: The grafting reaction was carried out at 100°C for 6 hours.

[0077] 2. Hydrophobic modification and hydrophilic regulation: 5% dodecyl bromide and 3% polyethylene glycol were added, and the reaction temperature was 75°C.

[0078] 3. Mixing and granulation: After mixing, granulation is carried out at 85°C to ensure good particle morphology.

[0079] Example 3:

[0080] Compared with Example 1, the difference is:

[0081] Materials and proportions:

[0082] Polyamide: reaction temperature 280°C, duration 10 hours.

[0083] Polyacrylic acid (PAA): molecular weight 80,000, weight ratio to polyamide 1:1.

[0084] NPK fertilizer: The mass ratio to modified polyamide is 0.01:1.

[0085] Preparation steps:

[0086] 1. Polyacrylic acid grafting reaction: The grafting reaction was carried out at 90°C for 5 hours.

[0087] 2. Hydrophobic modification and hydrophilic regulation: 15% dodecyl bromide and 7% polyethylene glycol were added, and the reaction temperature was 65°C.

[0088] 3. Mixing and granulation: Mixing and granulation are carried out at a temperature of 70°C.

[0089] Example 4:

[0090] Compared with Example 1, the difference is:

[0091] Materials and proportions:

[0092] Polyamide: reaction temperature 240°C, duration 14 hours.

[0093] Polyacrylic acid (PAA): molecular weight 110,000, weight ratio to polyamide 1:1.

[0094] NPK fertilizer: The mass ratio to modified polyamide is 0.05:1.

[0095] Preparation steps:

[0096] 1. Polyacrylic acid grafting reaction: The grafting reaction was carried out at 100°C for 4 hours.

[0097] 2. Hydrophobic modification and hydrophilic regulation: 10% dodecyl bromide and 5% polyethylene glycol were added, and the reaction temperature was 75°C.

[0098] 3. Mixing and granulation: Mixing and granulation were carried out at 85°C.

[0099] Example 5:

[0100] Compared with Example 1, the difference is:

[0101] Materials and proportions:

[0102] Polyamide: reaction temperature 275℃, duration 12 hours.

[0103] Polyacrylic acid (PAA): molecular weight 95,000, weight ratio to polyamide 0.75:1.

[0104] NPK fertilizer: The mass ratio to modified polyamide is 0.04:1.

[0105] Preparation steps:

[0106] 1. Polyacrylic acid grafting reaction: The grafting reaction was carried out at 95°C for 5 hours.

[0107] 2. Hydrophobic modification and hydrophilic regulation: 12% dodecyl bromide and 6% polyethylene glycol were added, and the reaction temperature was 70°C.

[0108] 3. Mixing and granulation: The mixture was granulated at 80°C.

[0109] Comparative experiment 1:

[0110] Objective: To evaluate the effect of polyacrylic acid grafting modification on the slow-release properties of polyamide-based fertilizers.

[0111] Experimental group: five different ratios of polyamide and polyacrylic acid were used to graft-modify the polymer (Examples 1-5).

[0112] Control group 1: pure polyamide without graft modification (100% polyamide).

[0113] Experimental steps:

[0114] 1. Sample Preparation: Graft-modified polymers were prepared and fertilizer granules were formed as described in Examples 1-5. Control Group 1 used the same method but without graft modification.

[0115] 2. Nutrient Release Test: Each sample was placed in standard test soil, maintaining the same soil moisture and temperature conditions. Samples were taken at set time points (1 day, 3 days, 7 days, 14 days, 28 days) to analyze nitrogen, phosphorus, potassium content in the soil solution.

[0116] 3. Data Recording: NPK concentrations at each time point were recorded to assess the nutrient release rate.

[0117] Experimental results are shown in the following table:

[0118]

[0119] From the data table, it can be observed that the graft-modified polyamides in Examples 1-5 significantly reduced the release rate of nitrogen compared to the control group, and this phenomenon was more pronounced with increasing polyacrylic acid content.

[0120] The higher molecular weight and lower proportion of polyacrylic acid in Example 1 (polyamide to polyacrylic acid ratio of 1:1) and Example 2 (ratio of 0.5:1) significantly affected the slow-release characteristics of the fertilizer, delaying the release of nutrients compared to the control group.

[0121] Examples 3, 4, and 5 also showed significant slow-release effects, indicating that even with lower molecular weight or higher proportion of polyacrylic acid, graft modification was effective.

[0122] From the experimental data, it is possible that the carboxyl groups (-COOH) introduced by grafting polyacrylic acid form stronger ionic bonds with ions in the fertilizer, making it more difficult for the fertilizer components to be hydrolyzed and eluted. In addition, the increase in carboxyl groups may also enhance the water absorption of the polymer, thereby affecting the release dynamics of the fertilizer.

[0123] By grafting polyacrylic acid to modify polyamides, the release rate of the fertilizer can be effectively controlled, providing a sustainable fertilizer solution for agriculture while reducing environmental pollution that may be caused by rapid nutrient release. The innovation of this method lies in optimizing the performance of the fertilizer through simple chemical modification, demonstrating the application potential of materials science in sustainable agricultural practices.

[0124] Comparative Experiment 2:

[0125] Objective: To evaluate the effect of hydrophobic and hydrophilic regulation through dodecyl bromide and polyethylene glycol addition on the slow-release characteristics of the fertilizer.

[0126] Experimental Setup:

[0127] Experimental group: different ratios of dodecyl bromide and polyethylene glycol and usage conditions in Examples 1-5.

[0128] Control group 2: Graft-modified polymer without hydrophobic or hydrophilic modification.

[0129] Experimental steps:

[0130] 1. Sample preparation: Polymers with different hydrophobic and hydrophilic modifications were prepared according to the description of Examples 1-5 to form fertilizer granules. Control group 2 used the same grafted polymer but without subsequent hydrophobic or hydrophilic modification.

[0131] 2. Nutrient release test: Each sample was placed in standardized test soil, maintaining the same soil moisture and temperature conditions. Samples were taken at set time points (1 day, 3 days, 7 days, 14 days, and 28 days) and the nitrogen, phosphorus, and potassium content of the soil solution was analyzed.

[0132] 3. Data recording: Record the NPK concentration at each time point to evaluate the nutrient release rate.

[0133] The experimental results are shown in the following table:

[0134]

[0135] As can be seen from the data table, the hydrophobic and hydrophilic modified polymers in Examples 1-5 exhibited significantly reduced nutrient release rates compared to the control group. This phenomenon indicates that hydrophobic and hydrophilic manipulation affects the release behavior of fertilizers by changing the physical and chemical properties of the polymers.

[0136] The hydrophobic modification (addition of dodecyl bromide) increases the hydrophobicity of the polymer matrix, making it more difficult for water to penetrate the polymer, thereby slowing down the dissolution and release of the fertilizer components.

[0137] Hydrophilicity regulation (addition of polyethylene glycol) increases the hydrophilicity of the polymer matrix, allowing water to enter more easily but by increasing the gel properties of the polymer, a more uniform hydration environment is formed, thereby controlling the diffusion and release of the fertilizer to a certain extent.

[0138] Example 5 showed the lowest nutrient release rate, which may be because the higher proportion of polyethylene glycol enhanced the gel properties of the polymer and effectively controlled the diffusion of nutrients. In addition, Examples 2 and 4 also showed good sustained-release performance after adding lower proportions of polyethylene glycol and dodecyl bromide.

[0139] The effectiveness of optimizing fertilizer release performance by chemically regulating the hydrophobicity and hydrophilicity of polymers provides a method for agricultural production to optimize crop nutrient utilization by controlling the fertilizer release rate, which can not only improve the economic benefits of fertilizers but also reduce the potential impact of fertilizer use on the environment.

[0140] Comparative experiment 3:

[0141] Objective: To evaluate the effects of different mixing ratios of NPK fertilizer and modified polymer on the slow-release properties of the fertilizer.

[0142] Experimental setup:

[0143] Experimental group: different mixing ratios of NPK fertilizer and polymer according to Examples 1-5 (from 0.01:1 to 0.05:1).

[0144] Control group 3: unmodified pure NPK fertilizer.

[0145] Experimental steps:

[0146] 1. Sample preparation: Fertilizer granules containing NPK fertilizer and polymer in different ratios were prepared according to the description of Examples 1 to 5. The control group used unmodified pure NPK fertilizer.

[0147] 2. Nutrient release test: Each sample was placed in standardized test soil, maintaining the same soil moisture and temperature conditions. Samples were taken at set time points (1 day, 3 days, 7 days, 14 days, and 28 days) and the nitrogen, phosphorus, and potassium content of the soil solution was analyzed.

[0148] 3. Data Recording:

[0149] The NPK concentration was recorded at each time point to assess the nutrient release rate.

[0150] The experimental results are shown in the following table:

[0151]

[0152] It can be seen from the experimental data that the different mixing ratios of the modified polymer and the NPK fertilizer in Examples 1-5 significantly reduced the nitrogen release rate, showing a significant slow-release effect compared to the control group.

[0153] Example 1 (polymer to NPK ratio of 0.03:1) showed the slowest nutrient release rate, indicating that higher polymer content significantly delayed nutrient release, likely because the high polymer concentration physically hindered nutrient dissolution.

[0154] Example 5 (polymer to NPK ratio of 0.04:1) showed a release rate close to the control group, but still had a certain degree of slow-release effect. This shows that even at a high fertilizer ratio, the modified polymer can still effectively control the release of nutrients.

[0155] Examples 2 to 4 showed a gradual increase in release rate, proportional to the respective fertilizer ratio, indicating that the ratio of fertilizer to polymer can be adjusted as an effective means of controlling the release rate.

[0156] By adjusting the mixing ratio of fertilizer and modified polymer, the release rate of fertilizer can be effectively controlled, providing a fine nutrient management method for agricultural production, which not only improves the economic benefits of fertilizer, but also reduces the potential impact on the environment. Through this way, the innovative slow-release technology shows the practical application potential of material science in agricultural practice.

[0157] Comparative Experiment 4:

[0158] Objective: To evaluate the comprehensive performance of modified polymer slow-release coating fertilizer in actual agricultural application, including the economic benefits of fertilizer, crop yield and environmental impact.

[0159] Experimental setup:

[0160] Experimental group: Different modified polymer slow-release coating fertilizers described in Examples 1-5.

[0161] Control group: Common slow-release fertilizers on the market.

[0162] Experimental steps:

[0163] 1. Prepare samples: Use the modified polymer formulations described in Examples 1-5 to prepare high molecular slow-release coating fertilizers, and use the conventional slow-release fertilizers purchased on the market for the control group.

[0164] 2. Plant the same variety of corn in a standardized farmland environment, apply different groups of fertilizers according to the recommended dosage. Record the health status, growth rate and final yield of the crops throughout the growing season.

[0165] 3. Environmental impact assessment: Measure the residual rate of fertilizer components in the soil and the nutrient loss of surrounding water bodies. Assess the long-term impact of fertilizer use on soil quality.

[0166] The experimental results are shown in the following table:

[0167]

[0168] From the data provided, the modified polymer slow-release coating fertilizers in Examples 1-5 showed the following advantages compared to the control group:

[0169] Crop yield: The yield of all examples was higher than the control group, with Example 5 showing the highest yield increase, indicating that the slow-release properties of the modified polymer may help crops absorb nutrients more efficiently, especially during critical growth periods. Example 4 also showed a significant increase in yield, which may be related to the nutrient release dynamics in the polymer formulation better matching crop demand.

[0170] Soil residue and water nutrient loss: The use of modified polymer high molecular slow-release coating fertilizer reduced soil residue rate and water nutrient loss rate, especially Example 5, which showed the lowest residue and loss, reducing the risk of nutrient waste and environmental pollution. This may be due to the polymer improving the adsorption and retention capacity of the fertilizer, reducing the loss of nutrients through surface runoff and leaching.

[0171] Growth cycle: The use of modified polymers also slightly shortened the growth cycle of crops, possibly due to more efficient nutrient supply promoting crop growth.

[0172] These results show that modified polymer high molecular slow-release coating fertilizer not only improves crop yield and growth efficiency, but also is environmentally friendly by reducing nutrient loss, demonstrating its potential application value in modern agricultural production. By optimizing the fertilizer formulation, economic benefits and environmental sustainability can be further improved, and the introduction of this innovative technology provides strong support for sustainable agricultural practices.

[0173] Although embodiments of the present application have been shown and described, it will be understood by those having ordinary skill in the art that various changes, modifications, substitutions and alterations can be made therein without departing from the principles and spirit of the present application, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a polymer sustained-release coating, characterized in that: The following steps are involved: The polyamide is dissolved in N,N-dimethylformamide, a polyacrylic acid solution is added, and benzoyl peroxide is added as a free radical initiator to carry out a grafting reaction; Dodecyl bromide is added to the grafted polymer to modify the hydrophobicity. After stirring for 0.5 to 1.5 hours, polyethylene glycol is slowly added to adjust the hydrophilicity. Stirring is continued for 2 to 4 hours.

2. The method for preparing a polymer sustained-release coating according to claim 1, characterized in that: The polyamide is prepared through the polycondensation reaction of caprolactam and water, and is cooled and cut into small particles. The polycondensation reaction temperature is 240-280° C. and the duration is 10-14 hours.

3. The method for preparing a polymer sustained-release coating according to claim 1, characterized in that: The molecular weight of the polyacrylic acid is 80,000 to 120,000.

4. The method for preparing a polymer sustained-release coating according to claim 1, wherein: In the polyacrylic acid grafting reaction, the weight ratio of polyamide to polyacrylic acid is 0.5:1 to 1:

1.

5. The method for preparing a polymer sustained-release coating according to claim 1, characterized in that: In the polyacrylic acid grafting reaction, the reaction temperature is 90-100° C. and the duration is 4-6 hours.

6. The method for preparing a polymer sustained-release coating according to claim 1, characterized in that: In the hydrophobicity modification and hydrophilicity regulation steps, the reaction temperature is 65-75°C.

7. The method for preparing a polymer sustained-release coating according to claim 1, characterized in that: In the hydrophilicity control step, the molecular weight of the polyethylene glycol selected is 3,000 to 5,000.

8. A polymer slow-release coating fertilizer, characterized in that: The polymer slow-release coating fertilizer comprises core NPK fertilizer particles and a polymer slow-release coating coated on the outside thereof, and the polymer slow-release coating is prepared by the preparation method according to any one of claims 1 to 7.

9. The polymer slow-release coating fertilizer according to claim 8, characterized in that The preparation of the polymer slow-release coating fertilizer comprises: mixing the modified polymer and the NPK fertilizer in a mass ratio of 0.01:1 to 0.05:1, granulating the mixture, and controlling the temperature at 70-90°C.

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